1. Field of the Invention
The present invention relates to a change discrimination device which detects and discriminates a change of a target including a feature on the earth, and more particularly, to a change discrimination device, a change discrimination method and a change discrimination program for detecting and discriminating a change of targets including features on the earth such as houses, structures, vehicles, roads, grounds and forests.
2. Description of the Related Art
Discrimination of a change (alteration) of a feature on the earth is required for grasping a state of a geographical change and a land use state. Features on the earth here include all, natural or artificial, objects on the earth such as grounds, forests, houses, structures, roads and vehicles. Although in the following, description will be made of discrimination of a change (alteration) of structures including houses, warehouses, factories and schoolhouses, the same description is applicable to discrimination of a change of grounds, forests and vehicles, and discrimination of a change of a feature on the earth is not limited to discrimination of alteration of a structure.
Alteration of a structure here represents a change caused by a loss of a structure, expansion/reform of a structure, new construction of a structure after destruction of a structure (new construction after destruction) and moving to or new construction at a lot with no buildings on it.
Among discriminations of an alteration of a feature on the earth, discrimination of an alteration of fixed assets such as structures including, for example, houses, warehouses, factories and schoolhouses is required to be accurate because they are taxable targets.
In addition, discrimination of an alteration of fixed assets is preferably automated for efficient work and labor-saving.
Examples of conventional methods for discriminating a change of a feature on the earth are recited, for example, in Japanese Patent Laying-Open No. 9-61164 (Literature 1) and Japanese Patent Laying-Open No. 2004-117245 (Literature 2).
Literature 1 recites the change discrimination support system for land use state and house shape which executes relative orientation, with one projectively transformed, two aerial photographs that are transformed into digital image data to each other and displays the image data having being projectively transformed in comparison, thereby reliably and efficiently executing discrimination of an alteration of fixed assets and entry of a kind of alteration by comparison of aerial photographs.
Literature 2, for example, recites the house alteration discriminating method which, with respect to each laser data including ground positional information and altitude information obtained for a predetermined region from the sky at two, new and old time points, enables automatic discrimination of an alteration of a house by sampling the altitude information on a mesh set based on the ground positional information to set a representative altitude value on each square of the mesh, and determining whether a house alters or not at the two, new and old time points, based on the number of squares to be discriminated in which a difference between representative altitude values of the squares at the new and old time points exceeds a threshold value set to be approximately one floor high.
The above-described conventional techniques, however, have the shortcomings set forth in the following.
According to the conventional art whose example is Literature 1, a kind of change of a height of a feature on the earth can not be discriminated. It is accordingly impossible to discriminate expansion of a structure in which the height of the structure is increased and reduction of a structure in which the height of the structure is decreased.
The reason is that image data as a target for change detection fails to include height information.
Another problem is that automatic detection of a change of a feature on the earth can not be executed with high precision.
The reason is that although image data as a target for change detection has color information, because even if no feature on the earth changes, a color change due to accumulated snow or a difference in a position of a shadow, for example, is detected to erroneously determine that a change occurs, an operator needs to confirm the determination.
In addition, taking aerial photographs at new and old time points from completely the same position is impossible and even if no change occurs, the same feature on the earth such as the same structure is erroneously determined to have a change because it is differently seen due to a difference in photographing conditions such as a scale, a focal length, an altitude and a photographing course.
Furthermore, according to the conventional art whose example is Literature 2, while a kind of change in a height of a feature on the earth can be discriminated, a change of a feature on the earth can not be detected to have a highly precise positional resolution.
The reason is that because laser data has a distance interval between required measurement points as long as several meters at the time of detecting a change in height and a distance interval between measurement points is not constant due to radial emission of laser, precise detection of a change of a feature on the earth is impossible at minute distance intervals.
A further problem is that a change of a structure having no change in height such as a structure newly constructed after destruction can not be detected.
The reason is that a change of a feature on the earth is detected only by height information.
A still further problem is cost higher than that required in detecting a change of a feature on the earth based only on an aerial photograph.
The reason is that when detecting a change of a feature on the earth to high precision, in addition to discrimination by a change in height, discrimination by a color change is indispensable and for that discrimination, an aerial photograph taken in the air is required in addition to laser data.
An object of the present invention is to solve the above-described problems of the conventional art and provide a change discrimination device, a change discrimination method and a change discrimination program which enable a change of a target including a feature on the earth to be discriminated while suppressing costs for change detection.